A former policeman turned cab driver was sentenced to life in prison yesterday for murdering a 25-year-old woman he had been 'obsessed' with.

Wan Kim-chung, 45, showed no emotion when, after two hours of deliberation, a jury of seven unanimously found him guilty of killing Jennifer Yu Wai-yuk in October 2010.

Wan, an ex-police constable who was working as a taxi driver at the time of his arrest, had told police that he and Yu were lovers, and that he had strangled her after she tried to break off the relationship when her German boyfriend returned.

'Only you know what happened between [the] 26th and 27th [of] October 2010,' said Mr Justice Andrew Macrae, of the Court of First Instance, when he imposed the mandatory life sentence on Wan.

'But it was clear from the jury's verdict that they rejected any suggestion from you that you were provoked to kill Yu.'

The judge said it seemed Wan was obsessed rather than in love with Yu, 18 years Wan's junior.

In a police interview played to the jury, Wan said Yu announced in his taxi that she would end their relationship, provoking him to strangle her. Wan also claimed that Yu repeatedly asked him for money.

Wan claimed he did not know that she was still alive when he tossed her half-naked body into the sea. The autopsy report concluded that Yu died by drowning.

Wan had earlier been convicted of indecent assault in March 1996 - shortly after his stint as constable from 1988 to 1995 - and was sentenced to 10 months in jail, the court heard after the verdict was delivered.

Wan's counsel said his client had been a hard-working taxi driver since 1995, though the lawyer acknowledged that no mitigation could prevent the mandatory jail sentence.

The counsel also cited evidence that Wan loaned HK$10,000 to Yu and even paid part of her credit card bill. Wan was clearly very much in love with Yu, and she encouraged him to meet her regularly, the counsel said.

Wan admitted most of the facts of the case and had offered to plead guilty to a lesser offence of manslaughter.

Outside the court, Senior Inspector Paul Wong Tak-choi, who was in charge of the case, said the verdict was the best of the possible outcomes. He said Wan had been telling a one-sided story about his relationship with the victim, which was unfair to Yu's family because the deceased could not refute it.